RAMPS Z-Axis problem

I'm currently building a Prusa i3 rework. I'm having a problem with the RAMPS board. When I only have one motor connected to the ramps z-axis It works great, no whining or skipping of steps. But when I add the other z-axis motor Both motors whine, skip steps and jiggle all over the place. I have adjusted the stepstick to no avail. I have tried other known working stepsticks and connected different motors all with the same problem. What could be the problem? Thanks in advance

I don't know much but it does sound like a low stepper current problem. Have you adjusted enough? Maybe you could try to run the motors without the rest of the axis to see if they can move without load. You could also be trying to run them too fast.
Keep in mind I'm no professional